Usually, in the manufacturing process of canned provisions, a can body is filled with beverage, food or other contents, a cap is placed thereon, the flange area of the can body and the curl area of the cap are double-seamed for sealing. A sealing composition is coated onto the curl area of the cap by means of a nozzle lining in advance of the seaming operation. The sealing composition fills in the very small spaces formed between the can body flange area and cap curl area after the double seaming operation in order to ensure the complete sealing of the can.
Conventional curing agent-free sealing compositions have a weakness in that they are easily squeezed out due to heat or external stress caused by a change in the inner pressure during the double seaming operation or high temperature sterilization step. In order to strengthen the squeeze-out resistance, there have been various sealing compositions formulated so as to make the formed layers hard at room temperature or so as to cure before the sealing operation. However, these other sealing compositions produce coatings that are too hard to obtain an appropriate seam thickness at the double seaming operation.
Typical known cap sealing compositions are disclosed in JP3-17872B, JP2888562B and JP2006-274168A.